An Hsp70 promoter drives expression of a ribozyme that is designed to cleave prd mRNA at a CUU site between nucleotides +304 and +305, downstream of the initiator ATG and 27 nucleotides upstream of the 5' intron/exon border. The ribozyme consists of a 24 base hammerhead catalytic centre flanked by 8-11 bases complementary to the prd mRNA target region.